Embodiments of the invention relate generally to power converters and, more particularly, to a bi-directional DC-DC power converter that processes and transfers differential power in a variable manner. The bi-directional DC-DC power converter processes power received thereby in a variable fashion, in both power flow directions, with a portion of the power received thereby being delivered directly to the other side of the converter without being processed.
Electric vehicles and hybrid electric vehicles are typically powered by one or more energy storage devices, either alone or in combination with an internal combustion engine. In pure electric vehicles, the one or more energy storage devices power the entire drive system, thereby eliminating the need for an internal combustion engine. Hybrid electric vehicles, on the other hand, include energy storage device power to supplement power supplied by an internal combustion engine, which greatly increases the fuel efficiency of the internal combustion engine and of the vehicle. Traditionally, the energy storage devices in electric or hybrid electric drive systems include batteries, ultracapacitors, flywheels, or a combination of these elements in order to provide sufficient energy to power an electric motor.
In electric and hybrid electric vehicles, energy may be transferred from one or more of these energy storage devices to a DC link coupled to a DC load (e.g., the electric motor). Typically, one or more DC-DC voltage converters (e.g., bi-directional buck/boost converters) are often employed to decouple the energy storage device voltage(s) from a DC link voltage (with the DC link being coupled to the electric motor), with one or multiple converters being employed to provide this decoupling. The bi-directional DC-DC voltage converters act to increase, or “boost”, the voltage(s) provided from the energy storage device(s) to the DC link to meet the power demands of the electric motor and act to decrease, or “buck”, the voltages generated from the electric motor during regenerative braking before providing the regenerative power to the energy storage device(s) to recharge the device(s).
While existing arrangements of bi-directional DC-DC voltage converters successfully allow for an increased supply of voltage to the DC link or a step-down of voltage to recharge energy storage device(s), certain drawbacks are associated with the use of such voltage converters. That is, in electric and hybrid electric vehicles, the typical DC-DC voltage converter that is provided is a full power rating DC-DC converter that includes switches which are employed in the power conversion process to carry the full power. In carrying the full power, the switches conduct higher current so as to generate more losses and also put higher requirements on the thermal management of the converter. Accordingly, the volume and weight of the system is further increased, and the cost of the system will also increase.
Previous attempts to address the issue of DC-DC converter inefficiency have focused mainly on utilizing improved DC-DC converter topology, design methodology, and component materials. However, each of these solutions can improve the performance of the vehicle system only by a limited amount and achieve these efficiency improvements only at an additional cost.
Therefore, it is desirable to provide a bi-directional DC-DC voltage converter having a reduced volume, weight, and losses and an increased efficiency, with the converter realizing an increased efficiency without associated cost increases.